Hi Lee, You got different values because ICC changed the interpretation of absolute intent and the Lab encoding from V2 to V4, and lcms2 is a V4 engine. To obtain same as lcms1 you need:
1) Set the global observer adaptation state to unadapted, as you are using absolute colorimetric intent. Just call cmsSetAdaptationState(0) before anything else. 2) use CreateLab2Profile for greater backwards compatibility. This only affect perceptual intent. Not needed in your case. 3) The Lab encoding has also been changed by ICC. You have cmsLabEncoded2FloatV2 and cmsFloat2LabEncodedV2 to deal with the old encoding. Additionally you can use TYPE_Lab_DBL and let the CMM to do the decoding for you. > LCMS1 values match very well those I get when using the Apple ColorSync > utility. lcms2 matches even better, it is just a matter of setting it up properly. Hope that helps Regards Marti El 28/01/2013 13:21, Lee Badham escribió: > Hi, > > I'm in the process of updating an application that uses LCMS to do colour > transformation to LCMS2 and have a problem. > > Converting a CMYK value to Lab gives quite different values using the same > profile and (as far as I can tell) the same settings. > > LCMS2 transform function is this: > > return > LCMS2TransformMBS.CreateTransform(p,LCMS2MBS.kTYPE_CMYK_16,lcms2labprofile,LCMS2MBS.kTYPE_Lab_16,3) > > LCMS1 Transform function is this: > > return > LCMSMBS.CreateTransform(p,LCMSMBS.TYPE_CMYK_16,lcmslabprofile,LCMSMBS.TYPE_Lab_16,3) > > where p is an opened CMYK ICC profile, lcmslabprofile and lcms2labprofile is > a simple CreateLab4Profile with no arguments. > > Using these transforms with a CMYK value of 0,0,0,0 (or any CMYK value) gives > different Lab Values - up to about 1.5dEab. > > Viewing the memoryblock I get back when calling the transform shows the > values are different too. > > LCMS1 values match very well those I get when using the Apple ColorSync > utility. > > Hope someone can help > > Regards, > > Lee Badham > > www.bodoni.co.uk | www.presssign.com > > > > ------------------------------------------------------------------------------ > Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, > MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current > with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft > MVPs and experts. ON SALE this month only -- learn more at: > http://p.sf.net/sfu/learnnow-d2d > _______________________________________________ > Lcms-user mailing list > Lcms-user@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/lcms-user > ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. ON SALE this month only -- learn more at: http://p.sf.net/sfu/learnnow-d2d _______________________________________________ Lcms-user mailing list Lcms-user@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/lcms-user
